In a display device, conventionally, a predetermined image can be displayed by utilizing light emitted from a light source that is installed inside the device (internal light source).
In recent years, as a result of popularization of mobile telephones, vehicle-mounted televisions and the like, there are increasing opportunities to view display devices in the outdoors; however, when a display device is viewed in the outdoor, there occurs a problem that the light intensity from an internal light source is lower than or equal to the light intensity of external light, and it is in many cases difficult to recognize a predetermined image.
Furthermore, for mobile applications such as mobile telephones, since the electric power consumption by an internal light source of a display device occupies a large proportion in the total electric power consumption, when the internal light source is heavily used, there is a problem that the duration of the battery is shortened.
Thus, in order to solve these problems, reflective display devices that utilize external light as a light source have been developed.
With such a reflective display device, since external light is utilized as a light source, a clearer image can be displayed as the external light is more intense, and the electric power consumption of the internal light source can also be effectively suppressed.
In a reflective display device, it is necessary to provide a film having a optical-diffusion function (hereinafter, may be referred to as an optical-diffusion film) inside the display device, in order to carry out display by utilizing external light.
Known examples of such an optical-diffusion film include a film provided with surface unevenness on the film surface (meaning the surface of a plane other than a cross-section of the film; the same applies throughout the following description), and a film having fine particles dispersed in the film.
However, when these optical-diffusion films are used, since the emission angle of diffused light is simply dependent on the incident angle of external light, there has been a problem that it is difficult to efficiently emit an external light incident from a wide range of angles toward the front of the display device as image display light.
Thus, there have been disclosed reflective display devices which use, unlike the optical-diffusion films described above, an optical-diffusion film that can control the emission angle of diffused light (see, for example, Patent Documents 1 and 2).
More specifically, reflective display devices are disclosed, which use a film that is formed by photocuring two or more kinds of polymerizable compounds having different refractive indices while phase-separating the polymerizable compounds, the film having a predetermined internal structure in which regions having a relatively high refractive index and regions having a relatively low refractive index are formed in a predetermined pattern within the film.
That is, Patent Document 1 discloses an electro-optic device in which an electro-optic material is sandwiched between a pair of substrates disposed to face each other, and a laminated structure diffusion film and a pillar-shaped structure diffusion film are provided on the outer surface side of any one substrate between the pair of substrates, while a reflector is provided on the other substrate side between the pair of substrates.
Here, it is disclosed that the laminated structure diffusion film used therein is a diffusion film in which plural resin layers having different refractive indices are alternately laminated, and the interfaces between these resin layers are formed to be inclined at a predetermined angle with respect to the film surface (or the back face).
Furthermore, it is disclosed that the pillar-shaped structure diffusion film used therewith is a diffusion film in which plural pillar-shaped resin layers having a low refractive index are provided within a resin layer having a high refractive index, and the interfaces between these resin layers are formed to be inclined at a predetermined angle with respect to the film surface (or the back face).
Furthermore, Patent Document 2 discloses a display device including a reflective display panel and an optical laminate disposed on the display panel, in which the optical laminate includes two or more sheets of anisotropic scattering films, and at least two sheets of films among the plural anisotropic scattering films have scattering central axes having mutually different transmittances.
Here, it is disclosed that the anisotropic scattering film used herein is a film having a louver structure or a pillar-shaped structure, each including two kinds of regions having mutually different refractive indices.